Vapor deposition apparatus



Oct. 29, 1968 Filed Aug. 3l, 1964 E. R. CAPITA VAPOR DEPOS IT IONAPPARATUS 3 Sheets-Sheet l L .l S 39 l i 38 INVENTOR.

5 4Sheeos-Sheet 2` E. R. CAPITA VAPOR DEPOSITION APPARATUSIllllllllllgillllll Oct. 29, 1968 Filed Aug.V 3l, 1964 Oct. 29, 1968 E.R. CAPITA VAPOR DEPOSITION APPARATUS 3 Sheets-Sheet I5 Filed Aug.- 3l,196,4

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United States Patent O 3,407,783 VAPOR DEPOSITION APPARATUS Emil R.Capita, Hudson, NJ. (7020 Hudson Blvd., North Bergen, NJ. 07047) FiledAug. 31, 1964, Ser. No. 393,253 Claims. (Cl. 11S-49.5)

The present invention relates to a means for vapor plating and moreparticularly to an improved vapor coating furnace of the type adapted toform a coating of a precisely controlled and uniform thickness. Thepresent invention is particularly characterized by its improved coatingthickness and uniformity, its reduction in any possible contamination,and its improved and more useful structure which simplifies operationand decontamination.

The present invention represents an improvement in this general type ofvapor coating apparatus wherein a uniformity of the coating thickness,an improved depth control, and a degree of purity of the coating areobtained which have not been heretofore achieved. In particular, theapparatus of the present invention is an improvement upon my copendingapplication Ser. No. 189,365, tiled Apr. 23, 1962, now Patent No.3,233,578.

Known vapor deposition coating processes reduce or decompose a volatilecompound on the heated surface of the object to be coated. Thehydrogen-reduction process, for example, passes hydrogen over a heatedliquid metal halide to provide a resulting mixture of hydrogen and themetal halide vapor. The mixture passes into a furnace coating chamberhaving a controlled pressure where it reacts at the heated surface ofthe object to be coated and deposits an adherent coating of thenonvolatile reaction product.

An important use of vapor deposition is in applying silicon coatings tosilicon discs or slices such as are used in the manufacture oftransistors. A silicon slice comprises the N-type and a silicon coatingon the slice comprises the P-type. The coating purity, the uniformity ofthe coating thickness, and the control of the coating depth are ofcritical importance in transistors. The apparatus of the presentinvention obtains these results in a simpler and more reliablemanufacturing operation to give a better product. The invention will nowbe described in a silicon coating operation although it is to beunderstood that it is not limited to such an operation and may be usedwith other coatings on other objects in a similar way.

Accordingly, an object of the present invention is to provideimprovements in vapor plating.

Another object of the present invention is to provide an improvedapparatus for vapor plating combining improved coating control andcontamination elimination with simplicity of furnace manufacture andoperation.

Another object of the present invention is to provide an improved vaporplating furnace which is safely and efficiently operated by relativelyinexperienced personnel.

Other and further objects of the invention will be obvious upon anunderstanding of the illustrative embodiment about to be described, orwill be indicated in the appended claims, and various advantages notreferred to herein will occur to one skilled in the art upon employmentof the invention in practice.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawings,forming a part of the specification, wherein:

FIG. l is a perspective view partially cut away of a preferredembodiment of the vapor plating furnace of the invention;

FIG. 2 is a vertical sectional view of the vapor plating furnace of FIG.1 taken along line 2-2 of FIG. l;

FIG. 3 is a top plan view of a Faraday shield for the apparatus;

3,407,783 Patented Oct. 29, 1968 ICC FIG. 4 is a sectional view of theFaraday shield taken along line 4-4 of FIG. 3;

FIG. 5 is a sectional view of a heating coil lead disconnect taken alongline 5-5 of FIG. l;

FIG. 6 is an enlarged detailed sectional view of the connection betweenthe rotating article support and the source of gas and vapor;

FIG. 7 is an exploded perspective of the support of FIG. 2;

PIG. 8 is a vertical sectional view of another embodiment of the vaporplating furnace; and

FIG. 9 is a plan View of another embodiment of the furnace of FIG. 8 forpolycrystal deposition.

The improved coating apparatus or furnace will first be describedgenerally with particular reference to FIGS. 1 and 2. As discussedabove, the process will be described in connection with the formation ofa silicon coating upon silicon slices in the manufacture of P-N typetransistor elements wherein the slices comprise the N-type and thesilicon coating comprises the P-type. The silicon slices to be coatedare illustrated at 1 arranged in spaced relation on the top of asusceptor 12 on a rotatable support 2.

An air-tight chamber is provided surrounding the support 2 andcomprising a removable cover 4 formed of a heat and corrosion resistantquartz. The cover 4 is removably mounted by means of an air-tight seal 5on a hollow and air-tight base 6. The gases used in the process to purgethe air-tight chamber and the vapor plating mixture are admitted to thechamber through a gas and power coupling 7 in base 6 and an exhaustoutlet 8 (FIG. l) is provided to evacuate 'the enclosure and to withdrawthe purging gases and the spent gases of the vapor coating mixture fromthe furnace.

The slices 1 are raised to the reaction. temperature before the vaporplating operation by a pancake-type induction heating coil 9 mountedbeneath the susceptor 12 and coupled to a high frequency power sourcethrough the coupling 10 in the base 6. The ring-like susceptor 12 ispreferably formed of molybdenum or pure graphite which is heated by thefield of the induction heating coil 9 and which transfers the heatenergy to the slices 1. During the heating and the plating operations,the entire support 2 including the susceptor 12 is rotated. The support2 includes a hollow support shaft 11 having an upper flanged portion 13and a lower drive portion 14.

The coating mixture of gas and vapor is directed upwardly through thehollow shaft 11 so that it flows radially outwardly over the slices 1which are being rotated on the susceptor 12 of the support 2. While thecoating mixture may be passed directly out of the flared outlet at thetop of the upper shaft portion 13, a preferred embodiment is illustratedin FIG. 2 wherein a feed tube 13 is mounted in the upper portion 13 ofthe shaft 11 having a anged outlet at its top so that the coatingmixture is released centrally but above the slices 1.. The uniformity ofthe coating thickness has been found to be improved by the use of arounded dome 16 positioned on support 2 below the feed tube 13. Thisdome 16' is also formed of a heat resistant material such as quartz anda preferred embodiment as illustrated is made up of an inner and outershell. As illustrated in FIG. 2, the ring-like susceptor 12 is removablyheld in place on a quartz support plate 15 and is held down on thesupport plate by a quartz hold-down plate 16. As seen in FIG. 7, theseplates 15 and 16 preferably have a generally triangular shape to furtherfacilitate the even flow of the coating mixture about the slices 1.

In order to further insure the uniform heating of the slices 1, theinduction heating coil 9 is mounted on an adjustable support plate 17 ofa suitable heat resistant insulating material such as quartz. Therelative position of the coil 9 with respect to the rotating support 2is adjusted by changing the lengths of the supports 18 which connect thecoil support plate 17 to the base 6.

It will be seen that a tine adjustment can bemade of the length of eachof the supports by rotating the nut portion 19 on the threaded portion20. The slice heating may be controlled by this adjustment of thespacing between the coil 9 and the susceptor 12 through a suitableadjustment of the length of the supports 18. In order to preventcorrosion and contamination Within the chamber, the heating coil 9 andthe connecting leads 21 and 22 between the coil 9 and the coupling 10are silver or silver coated. Both the leads 21 and 22 and the coil 9 arehollow tubes to permit a coolant to be passed through them during thecoating or epitaxial deposition operation.

The upper portion 13 of the shaft 11 for the support 2 is preferablymade of a material which is heat resistant and corrosion resistant suchas quartz. This upper portion 13 is threadedly coupled and sealed withan O-ring to a lower shaft 14 which also has a hollow center 24communicating with the hollow center of the upper portion 13 and whichcommunicates with the coupling 7 through bearing 26 as will be furtherdescribed below. The rotatable shaft 11 is supported by thrust bearing26 and axial bearing 25.

In order to insure an absolutely tight furnace chamber for the coatingoperation and to maintain a contamination-free coating zone bypreventing the entrance of impurities, a novel coupling plan for thedetachable shaft 11 is provided in the improved furnace as isillustrated in detail in FIG. 6. The inlet `line 27 for the coatingvapor is welded to the bottom of the furnace chamber at a suitableaperture 28 as illustrated at 29. This stationary vapor inlet line 27has the lower portion 30 of the coupling magnet 31 rotatably mountedthereon on a suitable bearing 32. The radial ange portion 33 of thethrust bearing 26 supports the weight of the support 2 together withbearing and fixes the height of support 2 in respect to the heatingcoils 9. In order to transmit the rotational drive of the lower magnetportion to the support 2 and to simultaneously provide a hold-down forceto improve the seal of the thrust bearing the upper portion 34 of themagnet 31 is flxedly attached to the support shaft 11 by the grippingnuts 36 and 37. The lower portion 30 of the magnet 31 is coupled to avariable speed drive motor through the reduction box 38 and gear train39 illustrated in FIG. l so that this portion of the magnet rotatesabout the stationary vapor inlet 27 at a predetermined speed. Thismotion is transmitted to the support 2 by the magnetic coupling betweenthe upper and lower portions of the magnet 30 as the upper portion 34rotates in synchronization with the lower portion 30.

Since the vapor inlet 27 is welded to the furnace base 6, itis clearthat the only possible source of vapor leakage in this gland is aroundthe surfaces of the thrust bearing 26. This leakage is eliminated oreffectively minimized due to the weight of the support 2 and themagnetic force which holds this bearing in place in the furnace base 6.Any leakage that does occur, however, will be seen to pass the vaporinto the furnace enclosure rather than into the surrounding atmosphere.Since this inlet is located in the lower portion of the furnaceenclosure adjacent to the vapor outlet 8, the vapor pressure on theinside of the bearing and within the shaft 11 will be greater than thepressure surrounding the outside of the coupling 7 so that any leakagewhich does occur will be outwardly so that there is no entry of vaporthrough the bearing 26 to the center of the hollow shaft 11. It is thusclear that the above described vapor entry and drive coupling provide anabsolutely leak proof and contamination proof vapor and power couplingfor the furnace.

The top of the base 6 is cooled by the inlet 41 which connects a sourceof coolant to cooling channel 42 and cooling tube 43 at the outer edgeof the base 6. The channel 42 and tube 43 connect to outlet 44.

As described above, the support 2 is continuously rotated during thevapor plating operation. The variable 4 speed drive motor 40 is adjustedduring the vapor plating operation to rotate the support 2 at speeds offrom about 5 to 30 r.p.rn. depending upon the thickness of the coatingbeing applied and other operating conditions.

The quartz jar 4 is preferably shielded by a Faraday shield 45 which iscooled by the tube 46 coupled to a coolant source by inlet 47 and outlet48, FIG. 3. The shield 4S is clamped to the jar 4 by an insulated andopen circuited ring-like clamp 49 (FIGS. 1 and 2).

Preferably, a cover 50 is positioned between the heating coil 9 and thesupport 2. This cover 50 which is formed of a heat resistantnonconducting material such as quartz reduces heat transfer from thesusceptor 12 to the water cooled heating coil and prevents thedeposition of silicon on the heating coil 9.

The base 6 and lower portion 14 of the shaft 11 are preferably made ofcorrosion resistant metal such as stainless steel.

In the vapor coating process described above it is particularlyimportant that absolute purity be maintained for the slices 1 prior tothe coating operation as well as for the surrounding elements of thefurnace and it is equally important that this purity be maintained inthe vapor coating formed during the coating process. The above describedstructure accomplishes this result with a high degree of eiciency,however, it has been found essential also to periodically perform athorough clean-out of the interior of the furnace and of the variouselements therein.

The improved furnace of my present invention has a novel arrangement ofits elements to permit such a decontamination including the provision ofreadily removable supporting elements for the electrical coils and forthe support elements for the slices including the vapor distributing anddirecting elements.

Referring to FIG. 2, the jar 4 is removably maintained on the base 6with its lower edge engaging the air tight seal 5. The jar or cover 4 istightly clamped in this position by a movable top clamp 51. When theclamp 51 is removed, the jar 4 together with its Faraday shield 45 islifted off so that the interior of the furnace is exposed. Thesupporting and vapor distributing support 2 is now easily removed since,as described above, this support 2 is rotatably mounted in the furnacewith the vertical shaft 11 supported in the base 6 by the two bearings25 and 26. The support 2 may therefore be removed by being simply liftedvertically from the bearings 25 and 26. The top plate 52 of the base 6is lifted from the furnace at the same time by removing the spaceddisconnect bolts 53 which hold the plate 52 onto the lower portion ofthe base 6. The support 2 and the base 6 may be removed as a unit. If itis desired to further disassemble these elements, the threaded couplingsbetween the upper and lower portions of the column 11 and the threadedconnection between the top magnet portion 34 and the lower portion ofthe shaft 11 may be disconnected. Prior to the lifting off of the plate52 the heat cover 50 for the induction heating coil 9 may be lifted fromits supports by the temporary raising of the support 2 and the heatingcoils 9 themselves are detached at the two disconnect couplings 53'(FIG. 5). As indicated above both the slices 1, the susceptor 12 and therelated hold-down weight 16 are readily removable since they are held inplace only by gravity in their normal operating positions.

FIG. 8 illustrates another embodiment of the improved vapor coatingfurnace, In the embodiment already described above, the vapors used inthe coating operation are distributed in an outwardly aring pattern fromthe hollow center 15 of the rotating support 2. The embodimentillustrated in FIG. 8 has a similar furnace enclosure or jar 60 with apancake-type induction heating coil 61 and an annular susceptor 62mounted on the rirn of a rotating support member 63,"In this embodiment,however, which is effective for extremely thin coatings the incomingvapor is applied to the moving slices from a stationary. vapor.distributor 64 having a vapor directing nozzle 65 positioned directlyabove one portion of the circular path of the moving slices 1. Y

The slices 1 are continuously heated by moving in circular pathimmediately above the circular induction heating coil 61. The slices 1pass directly beneath an intense concentration of the coating vaporduring a portion onlyof their rotation as they move beneath the vapordistributing nozzle 65.

The interior of the coating furnace is kept tight and secure againstcontamination by 'having tight seals for the entry of the electricalconduits 6 6 and the vapor conduit 64 and by using a magnetic clutch 67to transmit power to the rotating slice support 63.

A typical operating cycle for the above described coating apparatus ofFIGS. 1-7 will now be described.

With the quartz jar 4 removed from the base 6 by releasing clamp 51, thesilicon slices 1 which are to be coated are rst carefully placed on acleaned susceptor 12 and the susceptor 12 is placed on the support 2 andheld down by the plate 16. The quartz jar 4 is now placed on the seal 5on the base 6 and is clamped into position by clamp 51 to form anair-tight chamber. A vacuum is now drawn in the air-tight chambersurrounding the slices 1 of the order of about one micron. The chamberis next purged with nitrogen or an inert gas such as argon, neon, heliumand the like by passing it through the chamber between the coupling 7and the outlet 8.

A high frequency voltage source is connected to the induction heatingcoil 9 ranging from about 10 k.c. to about 450 k.c. adjusted to providepower in the range required for the various coating processes. A typicaltemperature range for applying silicon coatings is about 1190" C. tol450 C. The induction heating coil 9 now heats the molybdenum orgraphite susceptor 12 and the silicon slices 1 arranged around the edgesof the susceptor 12. The temperature of the slices 1 is observed bymeans of an optical pyrometer through a viewing surface 70 provided onthe jar 4. During the heating, the support 2 is rotated at speeds offrom 5 to 30` r.p.m. or higher to insure a uniform heating of theseveral silicon slices 1 and pure hydrogen is passed through the chamberbetween coupling 7 and outlet 8. A continuous supply of coolant ispassed through the coil 9 and the cooling channel 42 and tubes 43 and 46for the base and the Faraday shield 45 during the operation of theinduction heating coil 9. When the silicon slices 1 have reached atemperature of between 1190 and 1450 degrees C. the vapor plating iscommenced by the admission of hydrogen gas containing silicontetrachloride vapor through coupling 7. This mixture enters through theabove described conduits to the center of the rotating shaft 11 and itthen ows outwardly and over the heated slices 1 on the rotatingsusceptor 12 in a uniform pattern. When the mixture of hydrogen andsilicon tetrachloride vapor contacts the heated surfaces of the slices1, it reacts at the heated surface to deposit an adherent coating ofsilicon on each of the slices 1. In a typical silicon coating operation,the pressure in the chamber at the slices 1 is maintained at about 1 to2, p.s.i. above atmospheric pressure and the spent gases flow downwardlythrough the jar 4 to an exhaust zone within the base 6 adjacent tooutlet 8 which is kept at about atmospheric pressure by the continuousevacuation of the Spent gases through the exhaust outlet 8 to theatmosphere. This provides for a continuous ow of the mixture past theheated slices 1. The thickness of the silicon coating on the discs iscontrolled by controlling the pressure and the flow rates of an incomingmixture as well as the proportions of hydrogen and silicon tetrachloridein the mixture and by continuing the flow of mixture for a predeterminedtime. When this time period has elapsed, the supply of the vapor mixtureand the current to the heating coil 9 is cut off and the chamber isagain purged with nitrogen or argon or another inert gas and is openedby the removal of the jar 4 to provide access tothe coated discs 1 aftera suitable cooling period.

The embodiment illustrated in FIG. 8 and described above is operated ina generally similar manner including the loading and purging steps.During the actual coating process itself, however, the vapor isdirecteddownwardly onto the moving slices 1 in a concentrated zonedetermined by the vapor nozzle 65. The heated slices 1 move in acircular path above the induction heating coil 61 and continually passthrough this area of concentrated vapor at a constant speed as they turnon the rotating support 63. i

As described above, the coating is done with various mixtures of vaporsand gases with the composition depending upon the coating being applied.FIG. 9 illustrates another embodiment of the general type of furnaceillustrated in FIG. 8 which differs by having a plurality of nozzles 70positioned at the edge of a susceptor plate 71 for coating slices 72.Different vapors or gases may be applied from the various nozzles 70 inperforming a coating operation known as polycrystal deposition. Thisfurnace thus provides a further degree of llexibility of operation bypermitting this control of gas or vapor control through the variousspaced nozzles 70 in addition to the slice temperature and rotationalspeed control as described above. While three nozzles 70 are illustratedin FIG. 9, it is clear that any number of two or more may be used asrequired -for particular coatings.

FIG. 9 also illustrates double rings of slices 72 being coated on thesusceptor 71 and one nozzle 70 is positioned over each ring and thethird nozzle 70 is positioned in an intermediate position between thetwo rings of circularly arranged slices 72. This provides a coatingmeans of even greater capacity and exibility of operation.

It will be seen that significant improvements have been provided in ameans for vapor plating whereby a unique coupling is provided for theentry of vapor and for the rotational forces which cooperate with thearticle heating elements to provide for a uniform and pure vapor coatingof objects. The elements of the improved furnace are combined in aparticularly effective and novel manner to provide for improved coatingcharacteristics combined with an improved overall coating operationwherein the decontamination, loading and purging steps, which are animportant part of the overall process, are made more eficient and moreeasily performed,

As various changes may be made in the form, construction and arrangementof the parts herein. without departing from the spirit and scope of theinvention and without sacrificing any of its advantages, it is to beunderstood that all matter herein is to be interpreted as illustrativeand not in a limiting sense.

I claim:

1. Apparatus for vapor plating articles comprising the combination of asealed chamber; an induction heating coil in said chamber; anelectrically conductive article supporting susceptor mounted on arotatable hollow shaft adjacent said coil, said sha-ft adapted forconnection to a source of said vapor located externally of said chamberand having a vapor outlet disposed substantially equidistant yfrom andabove said susceptor; a vapor guide member disposed uniformly about saidhollow shaft and, from a location intermediate the vapor outlet and thearticle supporting surface of the susceptor, having a uniform wallportion extending from said shaft, downwardly and outwardly to saidsusceptor surface; a vertical thrust bearing for said shaft within saidsealed chamber for supporting the shaft, and a non-conducting heatresistant shield member intermediate said coil and said support.

2. The apparatus as claimed in claim 1 in which said susceptor comprisesa ring-like member, said susceptor being removably mounted on said shaftintermediate a support plate and a hold down plate, and :said platesbeing shaped to permit the passage of a portion of the vapor downwardlythrough the center of the ring-like susceptor.

3. The apparatus as claimed in claim 1 which further comprises a Faradayshield at least partially surrounding said chamber.

4. The apparatus as claimed in claim 3 in which said shield includesliquid cooling means.

5. The apparatus as claimed in claim 1 wherein means to drive saidhollow shaft comprises a magnetic couple.

References Cited UNITED STATES PATENTS 8 Van Leer et al. 118-49.1 XGoetzel et al.

Tassara 11,8-49 Theodoseau et al. A

117-107.1 X Auzolle 118-49 Spitzer et al 11S-48X Reuschel 11S-49.5 XCapita 118-49.1

CHARLES A. WILLMUTH, Primary Examiner.

MORRIS KAPLAN, Assistant Examiner.

1. APPARATUS FOR VAPOR PLATING ARTICLES COMPRISING THE COMBINATION OF ASEALED CHAMBER; AN INDUCTION HEATING COIL IN SAID CHAMBER; ANELECTRICALLY CONDUCTIVE ARTICLE SUPPORTING SUSCEPTOR MOUNTED ON AROTATABLE HOLLOW SHAFT ADJACENT SAID COIL, SAID SHAFT ADAPTED FORCONNECTION TO A SOURCE OF SAID VAPOR LOCATED EXTERNALLY OF SAID CHAMBERAND HAVING A VAPOR OUTLET DISPOSED SUBSTANTIALLY EQUIDISTANT FROM ANDABOVE SAID SUSCEPTOR; A VAPOR GUIDE MEMBER DISPOSED UNIFORMLY ABOUT SAIDHOLLOW SHAFT AND, FROM A LOCATION INTERMEDIATE THE VAPOR OUTLET AND THEARTICLE SUPPORTING SURFACE OF THE SUSCEPTOR, HAVING A UNIFORM WALLPORTION EXTENDING FROM SAID SHAFT, DOWNWARDLY AND OUTWARDLY TO SAIDSUSCEPTOR SURFACE; A VERTICAL THRUST BEARING FOR SAID SHAFT WITHIN SAIDSEALED CHAMBER FOR SUPPORTING THE SHAFT, AND A NON-CONDUCTING HEATRESISTANT SHIELD MEMBER INTERMEDIATE SAID COIL AND SAID SUPPORT.